I know why the error is the zeroes?

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Ous Chkiri
Ous Chkiri 2019-11-7
编辑： Hiroki Okawa 2019-11-8
clear all;
close all;
clc;
dt=0.25;
x=-40:450;
ui=0.5.*exp(-log(2).*(x./3).^2);
figure(1)
plot (x,ui)
xlabel('x-axis')
ylabel('u(x,0)')
xlim([-40 450])
ui=0.5.*exp(-log(2).*((x-400)./3).^2);
figure(2)
plot (x,ui)
xlabel('x-axis')
ylabel('u(x,400)')
xlim([350 450])
ylim([-0.2 0.6])
%%Central difference
unew=zeroes(1,471);
uold=ui;
for j=1:1600
unew(1)=uold(1)-dt*((uold(2)-uold(1))/2);
for i=2:length(ui)-1
unew=uold(i)-dt*((uold(i+1)-uold(i-1))/2);
end
uold=unew;
j*dt;
end
figure
plot(x,ui(x,400))
hold on
plot(x,unew)
hold off
title('central difference @dt=0.25')
  2 个评论
Star Strider
Star Strider 2019-11-7
Not spelled correctly. Should be:
unew = zeros(1,471);
darova
darova 2019-11-7
unew has no index?
unew=uold(i)-dt*((uold(i+1)-uold(i-1))/2);

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回答（1 个）

Hiroki Okawa
Hiroki Okawa 2019-11-8
编辑：Hiroki Okawa 2019-11-8
1.
% unew = zeros(1,471);
unew = zeros(size(ui));
2.
% unew=uold(i)-dt*((uold(i+1)-uold(i-1))/2);
unew(i)=uold(i)-dt*((uold(i+1)-uold(i-1))/2);
3.
% plot(x,ui(x,400))
plot(x,ui)

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